var practice = function(){
/*
	//01.
	var $divs = $("div");
	console.log("div length : "+$divs.length);
	$divs.css("border", "1px solid #ff0000");
	
	//02.
	var $div2Child = $("div:eq(2) div");  
	$div2Child.css("border", "1px solid #ff0000");
	
	//03.
	var $contentData = $(".content_data");  
	$contentData.css("border", "1px solid #ff0000");

	//04.
	var $header = $("#header");  
	$header.css("border", "1px solid #ff0000");
	
	//05.
	var $nodes1 = $("body").contents();
	console.log("body contents length ? "+$nodes1.size()); //3
	     
	var $nodes2 = $("body").children();
	console.log("body children length ? "+$nodes2.size()); //1
	 
	var $nodes3 = $("#sample_page").children();
	for(var i=0;i<$nodes3.length;i++){	     
		var $node = $nodes3.eq(i);
	    $node.css("border", "1px solid #ff0000");
	}	   

	//06.	
	var $firstChild = $("div#sample_page").children().first();
	var $lastChild = $("div#sample_page").children().last(); 
	$firstChild.css("border","1px solid #ff0000");
	$lastChild.css("border","1px solid #00ff00");	

	//07.
	var $header = $("#header");  
	$header.parent().css("border", "1px solid #ff0000");
	$("#data_1").parent().css("border", "1px solid #ff0000");

	//08.
	$("#data_1").parents().css("border", "1px solid #ff0000");

	//09.
	$("#data_1").parents("#sample_page").css("border", "1px solid #ff0000");
	
	//10.
	var $content = $("#content");
	$content.prev().css("border", "1px solid #ff0000");	  
	$content.next().css("border", "1px solid #00ff00");

	//11.
	var $content = $("#content");	
	var $p1 = $("<p>add1</p>");
	var $p2 = $("<p>add2</p>");
	var $p3 = $("<p>add3</p>");
	var $p4 = $("<p>add4</p>");
	var $p5 = $("<p>add5</p>");
	var $p6 = $("<p>add6</p>");
	
	$content.css("border","1px solid #00ff00");	
	$p1.css("border", "1px solid #ff0000");
	$p2.css("border", "1px solid #ff0000");
	$p3.css("border", "1px solid #ff0000");
	$p4.css("border", "1px solid #ff0000");
	$p5.css("border", "1px solid #ff0000");
	$p6.css("border", "1px solid #ff0000");
	
	$content.before($p1);	
	$p2.insertBefore($content);
	$content.append($p3);
	$p4.appendTo($content);
	$content.after($p6);
	$p5.insertAfter($content);

	//12-1.
	var $p = $("p#data_1");
	var $clone = $p.clone();
	$clone.css("border","1px solid #ff0000");
	$clone.insertBefore($p);
	
	//12-2.
	$clone.remove();
*/
	//13.
	var $content = $("#content");
	var $header = $("#header");
	$content.css("border","1px solid #00ff00");
	$header.css("border","1px solid #ff0000");
	$header.appendTo($content);
};

$(practice);